1. Field of Invention
This invention relates to a method for accurately metering a precise increment of liquid and to apparatus for carrying out the same. It is particularly directed to a method and apparatus in which a precise increment of liquid is admitted into a collapsible chamber together with a quantity of air and the mixture of air and liquid discharged from the chamber through a nozzle by collapsing the chamber. Still more particularly the invention is directed to an improved method and apparatus for effecting serial dilution in which the increment of liquid to be diluted and air are drawn into an elastic tubing and both the air and the liquid are simultaneously discharged from the tubing through a nozzle into a measured amount of dilution liquid by collapsing the elastic tube, and in which the process is repeated as needed to effect the desired number of serial dilutions.
2. Prior Art
Serial dilution has heretofore been effected by drawing the liquid to be diluted into a syringe to a predetermined volume and thereafter squirting it into a measured volume of dilution liquid and repeating this operation step by step until the desired number of serial dilutions is effected. This method and apparatus has the disadvantage that even if the plunger stroke of the syringe is limited by means of end stops in order to permit some automization of the function, the inevitable leakage at the plunger packing could bring about a systematic volume error which is unacceptable in the handling of small liquid volumes, for example, of a magnitude of 25 to 50 microliters. Furthermore, any attempt to cushion the drawing in and expulsion strokes in automated apparatus is likely to introduce errors in the amount of liquid measured out, especially when very small liquid volumes are involved.